There are two principal types of refrigeration systems generally in use, namely, compression refrigeration systems and absorption refrigeration systems.
The most well-known refrigeration systems are the compression systems used in most home refrigerators and home air-conditioning systems. A refrigerant, such as Freon or ammonia may initially be in the liquid state, under pressure. It is then passed through an expansion valve where it evaporates and becomes a gas with a very substantial drop in temperature. Air is normally blown past coils or pipes through which the evaporating refrigerant is flowing, and the cold air cools the refrigerator or the home. The warmed gas is then routed to an electric compressor, which further heats the gas as it is compressed. The hot compressed gas is then routed to a cooling tower or condenser, where the compressed refrigerant reverts to the liquid state as it is cooled. The cooling cycle is then repeated.
Absorption system refrigeration circuits are somewhat more complicated. They use a refrigerant such as ammonia, and an absorbent, such as water. As in the compression circuit described above, cooling is accomplished when the liquid refrigerant goes through an expansion valve and is permitted to evaporate, with the expected substantial reduction in temperature, and is used for cooling. The vaporized refrigerant, which has now increased in temperature, then flows to an absorber where it is restored to liquid form by being dissolved in the liquid absorbent, such as water, with the substantial generation of heat, normally removed by cooling water or air when water is not available. The liquid solution of absorbent and refrigerant are then raised to a high pressure by a pump, and routed to a still, or other arrangements such as a reboiler and fractionating column combination, wherein external heating is supplied to separate the ammonia (refrigerant) from the water (absorbent). The hot gaseous ammonia at relatively high pressure is then routed to a condenser where it is cooled and liquefied. The cycle is then repeated.
Normally power is supplied from commercial sources to power the pumps or compressors in refrigeration circuits. However, in some systems, such as that disclosed in U.S. Pat. No. 4,335,580, heat from the coolant system of an engine is employed to at least heat the refrigerant when it is functioning in a reverse cycle in the "defrost" mode of the unit. Also, U.S. Pat. No. 4,380,909 discloses the use of heat from engine exhaust gases in an absorption cycle heat pump system. Also to be noted are prior systems in which a single refrigerant is employed in both compression and absorption refrigeration modes, see U.S. Pat. Nos. 4,505,133, 4,031,712, and 4,285,211.
However, the foregoing systems have significant problems, and substantially lower efficiency than would be desirable. In addition, it is not possible with Freon systems and not practical in most cases to retrofit existing refrigeration systems to conform with ammonia systems with the teachings of the foregoing cited patents.
Accordingly, a principal object of the present invention is to provide an improved refrigeration system which is substantially more efficient than existing systems, and which may be readily retrofitted onto existing systems, whether Freon, ammonia, or other refrigerants are used.